2015 Annual Report Selected Highlights

A Better Understanding of how Antibiotic Resistance Spreads Among Bacteria

Around the globe, antibiotic-resistant bacteria render common healthcare-associated infections difficult, and at times, nearly impossible to treat. To advance understanding of this growing issue, researchers from the NIH Clinical Center and the National Human Genome Research Institute oversaw a two-year genomic and epidemiologic collection of more than 1,000 patient surveillance cultures and more than 400 environmental samples within the research hospital. They discovered that some bacteria are exchanging genes that cause antibiotic resistance.

In their paper, published in Science Translational Medicine, researchers described how they used a powerful new form of DNA sequencing to study the complete genome of bacteria samples and identify their antibiotic-resistance genes. They found that antibiotic-resistance genes could move from one bacterial species to another through the exchange of plasmids – small, mobile pieces of DNA – and thus transfer the ability to inactivate certain antibiotics.

This was among the first studies to use such detailed genomic sequencing methods to look at plasmid transfer in a hospital environment, and it demonstrated how the action may be contributing to the increase in antibiotic-resistant bacteria around the world.

The study showed the tremendous value of accurate whole-genome sequencing to differentiate bacterial transmissions within the hospital from introductions of multidrug-resistant bacteria in patients who acquired them before admission to the Clinical Center.

Overall, only a few bacterial isolates had swapped their antibiotic-resistance genes. Many plasmids carrying these genes are incompatible with each other or with some bacterial strains. Understanding the ground rules regulating plasmid trafficking is one of the most important research topics the NIH is currently involved in.

Regardless of the source of drug-resistant bacteria, the Clinical Center takes rigorous steps to monitor and minimize the spread of these infections. The Clinical Center performs approximately 15,000 surveillance tests per year, with some areas being tested twice weekly and others on a monthly basis. A positive culture of an antibiotic-resistant bacteria is found less than one percent of the time.

The NIH is committed to preventing healthcare-associated infections, isolating patients who are carriers of the bacteria, containing these bacteria when they do arise and researching global applications to prevent, treat and cure them.

More information: www.ncbi.nlm.nih.gov/pubmed/25232178

Plasmid transfer between bacterial species
Plasmid transfer between bacterial species can be investigated with single-molecule DNA sequencing technology. Plasmids, small circular mobile pieces of DNA seen in these three bacteria, can carry genes encoding resistance to antibiotics, including carbapenems, a powerful class of antibiotics used to treat serious infections. The bacterium on the left has a circular plasmid that moves to the bacteria in the middle. Once there, it acquires the second bacteria's unique gene for antibiotic resistance and continues to transfer that genes characteristics to the third bacteria, thus spreading the ability to resist antibiotics. Credit: Darryl Leja, National Human Genome Research Institute NHGRI/NIH.

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